The present invention relates to the field of printing presses and, in particular, to an apparatus for folding signatures in the folder section of a printing press.
The printing industry is continually increasing the speed at which printed copies can be generated. Printing, forming, folding and cutting operations are often done by a continuous operation machine, feeding in a web of blank paper from a roll and ending with a printed, cut and folded product, often referred to as a signature. For example, a web may pass through a series of processing units such as the print units, dryer, chill unit, folder and stacker, among others, in being processed into a finished product. One such processing unit in the folder is the quarterfolder.
Quarterfolding is typically defined as, for example, folding occurring in the web direction after the signature or sheet has been cut off from the web. The signature may also have been folded prior to quarterfolding. Typical quarterfolding is done, for example, by presenting signatures in sequence to a chopper mechanism that descends upon the signature, forcing it downward through a slot into awaiting rollers which fold the signature. Signatures typically are presented for quarterfolding at a 50% duty cycle, that is, there is a signature of a specific length followed by a space of approximately equal length before the next signature. Therefore, the chopper mechanism descends upon signatures which are presented one half of the cycle time.
Quarterfold mechanisms are known in the art. For example, U.S. Pat. No. 4,509,939, incorporated herein by reference, purportedly discloses a quarterfold folding device having a quarterfold blade arranged parallel to the direction of forward travel of a signature and intended to introduce the signature between two rotating cylinders parallel to the direction of forward travel, so as to form the longitudinal fold in the signature. The quarterfold folding device is purportedly suspended from two drive cranks which are rotationally driven parallel in the same direction and at the same speed by means of two additional rotating cranks, each of which is connected to one end of the drive cranks by means of a rotating pivot. The drive cranks carrying the quarterfold blade purportedly drive the quarterfold blade in a vertical movement between a bottom position and a top position. Signatures are purportedly fed into the quarterfold mechanism in a sequential and periodic manner corresponding to the period of the blades movement from the top position to the bottom position.
The process of quarterfolding is limited in speed, however, by the rates at which mechanisms and signatures can be treated with a 50% duty cycle as described above. To achieve higher speeds, two separate quarterfolders can be configured on one folder and, for example, arranged so that each quarterfolder folds alternating signatures. This approach adds costs and space requirements, however, that may be prohibitive to many smaller presses thereby limiting their potential speed.
It is an object of the present invention to provide a quarterfold folding device and method wherein selected signatures in a stream of signatures are delayed to form signature groupings, such as signature pairs, which are then folded via an appropriately sized chopper blade or folding blade, wherein the speed that the signatures are conveyed and the chopping rate can be varied as a result of forming the signature groupings.
Thus, the method and device according to the present invention achieves higher signature throughput by performing one quarterfold cycle for multiple signatures while using a single quarterfolder. Signatures are grouped into, for example, pairs and then the group of signatures is quarterfolded with an appropriate length single chopper blade, for example an extended length chopper blade. Thus, the quarterfolder according to the present invention can receive signature pairs at increased signature rates and at a 50% duty cycle, thereby increasing signature through-put. The device according to the present invention is usable in folders or sheeters performing a cross fold in a sheet or signature by a chopper mechanism.
The quarterfolding process according to the present invention involves delaying, for example, alternate signatures on their way to the quarterfolder, such that every other signature is moved back to create a smaller space behind it and a greater space ahead of it. This greater space allows a chopper mechanism to maintain, for example, a 50% duty cycle, while increasing the number of signatures that are quarterfolded in a given time or decreasing the chopping rate while quarterfolding the same number of signatures in a given time or some combination of both. The signatures that are simultaneously processed are paired by, for example, a delaying process. A suitable signature delaying mechanism may group the signatures as desired to prepare them for the quarterfolding process.
Thus, an exemplary embodiment of the present invention provides a chopper blade or quarterfold blade that is approximately twice the length of a single signature, wherein by controlling the feed rate at which the stream of signatures are fed to the quarterfold blade and delaying certain signatures, a grouping of signatures, for example, a pair, are quarterfolded simultaneously by a single blade without increasing the chopping rate of the blade.
The quarterfold folding device may also include a system for balancing the dynamic forces generated by the moving quarterfold blade as described in U.S. Pat. No. 5,458,557 entitled xe2x80x9cQuarter-Fold Folding Device Having a Balancing System,xe2x80x9d which is incorporated in its entirety herein by reference.
The following description regarding the appended drawings, given by way of non-limiting examples, describes the present invention and how it can be produced.